One of the projects of the Single European Sky Air Traffic Management Research is to improve the crew awareness when the ownship (which may be an aircraft or a ground vehicle) deviates from a taxi-clearance assigned by air traffic control (ATC).
Any system providing a solution will have a problem addressing when a vehicle deviates from the taxi clearance in an intersection area. Especially in the case of a small angle between intersecting taxiways (causing a big turn), the real trajectory and maintained turn radius of ownship fully depend on the flight crew and are “unpredictable” for any system onboard the ownship. Monitoring change of ownship heading and position during the turn is not feasible, due to the fact that the ownship can start the turn by turning to the opposite direction, see FIG. 1-1. How much ownship turns and goes to the opposite direction before it starts turning on the assigned taxiway fully depends on the technique used by the flight crew.
FIG. 1-2 is an aerial photograph of an airport taxiway intersection showing various tire marks in several locations, and presents evidence that different airplanes make the same turn with different radii (trajectory). The challenge is to provide an alert, if the crew makes a significant deviation from the assigned clearance, while permitting normal maneuvering without providing unwanted alerts.